Chapter 33B: Flatworms and Annelids

Characteristics of Lophotrochozoans

Bilateria

Triploblastic

Digestive tract with two openings

Ex: flatworms, rotifers, ectoprocts, brachiopods, mollusks, annelids

Lophophore

naming of Lophotrochozoans

meaning: crown of tentacles that function in feeding

Trochophore

naming of Lophotrochozoans

meaning: distinct larval stage

Phylum Platyhelminthes — Flatworms

Lophotrochozoan;

Habitats: marine, freshwater, damp terrestrial

Free living = Planarians

Parasitic = Tapeworms and Flukes

Size: microscopic → 20 meters

Acoelomates

~Platy

~flat

~helminth

~worm

Protonephridia

flatworms;

maintain water balance

How do flatworms move?

via cilia and muscles

Four classes of flatworms

Turbellaria (free-living)

Monogenea (monogeneans)

Trematoda (trematodes, flukes)

Cestoda (tapeworms)

Turbellaria

four classes of flatworms;

free-living flatworms

ventral nerve cords that run the length of the body

incomplete digestion system via pharynx

ganglia at the anterior end of the worm

Ex: Planarians

First true cephalization

flatworms;

cephalis = head

Light sensitive eyespots

flatworms;

first eyes

Cephalic ganglion

flatworms;

first nervous system

Hermaphrodites

flatworms;

sexual or asexual

Monogenea

four classes of flatworms;

parasitic flatworm

parasites of fish

Trematodes

four classes of flatworms;

flukes

parasites of humans

part of life cycle in snail hosts

Ex: liver flukes, blood flukes

Liver flukes

trematodes;

obtained by eating raw fish

causes Cirrhosis

Blood flukes

trematodes;

causes Schistosoma/schistosomiasis

second most devastating parasitic disease (first is Malaria)

oral and ventral suckers for attachment to host

Cestoda — Tapeworms

four classes of flatworms;

parasites of vertebrates

no mouth/digestive system

Scolox “Holdfast”

Proglottids: reproductive segments

obtained by eating beef/pork tapeworms → blocks intestines

Phylum Annelida — Annelids

Lophotrochozoan;

two clades: Errantia and Sendentaria

Clade Errantia

Annelids;

most are mobile/marine

predators and grazers (algae)

segmented body

Trochophore: Ciliated Larva

Features of a segmented body in Clade Errantia

Parapodia: paddle-like, located beside feet; locomotion, protection, gas-exchange

Cirri: long, sensory organs

Clade Sedentaria

Annelids;

less mobile

Sedere ~to sit

Ex: Christmas Tree Worm, leeches, earthworms

Leeches

Clade Sedentaria;

mostly freshwater

some suck blood from animals

predators that feed on other invertebrates

Hirudin

Hirudin

leeches;

chemical secreted to keep blood from coagulating

bloodletting, surgical use

Earthworms

Clade Sedentaria;

soil habitat

eat organic matter

100-175 segments

Hermaphrodites but can cross fertilize